1. Field of the Invention
This invention relates to analyte level detection and monitoring in tissue. More particularly, this invention relates to methods for noninvasively detecting and monitoring the analyte concentration in tissue, body fluid such as blood, and implants using optical coherence tomography. The analyte concentration may include glucose concentration.
2. Description of Related Art
Approximately 14 million people in the United States, and more than 120 million people all over the world suffer from diabetes mellitus (commonly referred to as xe2x80x9cdiabetesxe2x80x9d or xe2x80x9cWillis"" diseasexe2x80x9d), a chronic, systemic, metabolic disease that is the most common disorder of the endocrine system. The disease is brought on by disorders in blood levels of insulin, a pancreatic hormone that helps convert glucose, or blood sugar, into energy. Insulin is necessary for glucose to go from the blood to the inside of the cells, and unless the glucose gets into the cells, the body cannot use it. The excess glucose remains in the blood and is then removed by the kidneys.
Type 1 diabetesxe2x80x94sometimes called insulin-dependent diabetes mellitus (IDDM), or juvenile-onset diabetesxe2x80x94results from a shortage of insulin. With IDDM, the pancreas makes little or no insulin because the insulin-producing beta cells have been destroyed. IDDM usually appears suddenly and most commonly in younger people under age 30. Type 2 diabetesxe2x80x94also known as noninsulin-dependent diabetes mellitus (NIDDM), or adult-onset or stable diabetesxe2x80x94results from the body""s inability to process insulin effectively. With NIDDM, the pancreas makes some insulin, and sometimes too much. However, the insulin is not effective because of its resistance by muscle cells. About 90 to 95 percent of all people with diabetes have Type 2 diabetes.
The complications of diabetes can demand as much attention as the disease itself. Most importantly, diabetes sufferers must monitor their blood sugar levels everyday to prevent an attack of hypoglycemia, in which available levels of blood sugar are too low to fulfill the body""s energy needs. Hypoglycemia can easily be remedied, however, once its symptoms, such as weakness, dizziness, tingling in the hands and feet, and rapid heartbeat, are recognized. Diabetes may even result in a coma and causes about 60,000 deaths in the United States every year.
Long-term complications from diabetes can damage the eyes, nervous system, kidneys, and cardiovascular and circulatory systems, as well as hinder the body""s overall resistance to infections. Cuts and sores heal more slowly for people with diabetes, who are also prone to gum problems, urinary tract infections, and mouth infections such as thrush, caused by an overgrowth of yeast organisms.
The proper treatment of diabetes includes maintenance of blood glucose at normal levels. Presently, the method by which diabetic patients control their blood glucose levels involves a finger puncture several times a day to obtain a droplet of blood for further chemical analysis. This inconvenient, invasive procedure limits the frequency of monitoring and, therefore, may give inadequate control of the long-term complications of the disease. The removal of this daily constraint would considerably improve the quality of life for diabetic patients, facilitate their compliance for glucose monitoring, and reduce complications and mortality caused by the disease. Thus, a noninvasive, quantitative method for monitoring blood glucose levels would be of great importance and would offer many people an improved way of life.
There have been significant efforts by many companies and scientific groups to monitor blood glucose concentration noninvasively using various, specific optical approaches: polarimetry, Raman spectroscopy, near infrared (NIR) absorption spectroscopy, and NIR scattering. Although each of these techniques has demonstrated at least a degree of utility in detecting glucose levels, shortcomings remain. In particular, each known method has unfortunate, inherent limitations: (1) low sensitivity (signal-to-noise ratio) for the glucose concentrations at clinically-relevant levels, and (2) insufficient specificity of glucose detection that requires development of complex algorithms for analysis of multicomponent systems. In other words, the methods currently known (1) cannot provide adequate sensitivity to reliably and accurately monitor glucose levels typical in clinical situations and (2) cannot detect glucose reliably and accurately without resort to complicated analytical schemes that often rely upon several components, and which may add extra expense and undue complexity to the glucose-monitoring process. Thus, although current techniques may have demonstrated limited success in monitoring glucose levels, room for significant improvement remains. In particular, reducing or eliminating the limitations of the existing techniques would be very beneficial. More particularly, providing methods for detecting glucose levels within tissue in an accurate, reliable, and relatively simple manner would be advantageous.
Problems enumerated above are not intended to be exhaustive but rather are among many that tend to impair the effectiveness of previously known glucose-detection techniques. Other noteworthy problems may also exist; however, those presented above are sufficient to demonstrate that prior techniques appearing in the art have not been altogether satisfactory.
The present invention provides an optical coherent tomography (OCT) apparatus including a radiation source, a probe arm for directing a portion of the radiation into a tissue, body fluid such as blood, or an implant in an animal including a human, a collector for collecting reflected or back scattered light from the tissue, an interferometer having a first input for receiving the reflected or back scattered light and a second input for receiving source radiation from a reference arm and a detector for measuring the interference signal of the reflected light and correlating the signal to a glucose concentration.
The present invention also relates to a method for measuring blood glucose levels including directing a portion of radiation from a radiation source onto a tissue site of an animal including an human, collecting a reflected or back-scattered light from the tissue, feeding the reflected light and a second portion of radiation from the radiation source into an interferometer, measuring an interference signal and the signal to a glucose concentration.
The present invention also provides as method implemented on a computer for analyzing interferometer data and correlating the data to a glucose concentration.
In one respect, the invention is a method for measuring glucose concentration within a tissue. Radiation is generated. A first portion of the radiation is directed to the tissue to generate backscattered radiation. A second portion of the radiation is directed to a reflector to generate reference radiation. The backscattered radiation and the reference radiation is detected to produce an interference signal. The glucose concentration is calculated using the interference signal.
In other respects, the generating radiation may include generating low-coherence radiation. The generating low-coherence radiation may include generating low-coherence radiation using a super-luminescent diode. The generating radiation may include generating radiation from a plurality of sources. Two or more of the sources may be used to emit radiation having different wavelengths. A wavelength of the backscattered radiation may be substantially equal to a wavelength of the reference radiation. The radiation may have a first polarization and the backscattered radiation may have a second polarization, the second polarization being different from the first polarization. The tissue may include skin. The tissue may include a blood vessel. The tissue may include sclera. The tissue may include lip. The tissue may include tongue. The tissue may include oral tissue. The tissue may include ear. The backscattered radiation may emanate from a tissue depth of between about 150 microns and about 500 microns. The backscattered radiation may emanate from a tissue depth of between about 150 microns and about 400 microns. The backscattered radiation may emanate from a tissue depth of between about 150 microns and about 200 microns. The directing a first portion of the radiation may include scanning the first portion of the radiation across a specified portion of the tissue. The calculating may include determining the glucose concentration using a slope of the interference signal. The calculating may include determining a glucose-induced change in an optical property of the tissue. The optical property may include scattering, anisotropic factors, absorption, or index of refraction. The calculating may include determining a glucose-induced change in morphology of the tissue. The morphology may include thickness or shape.
In another respect, the invention is a method for measuring analyte concentration within a tissue. Radiation is generated. A first portion of the radiation is directed to the tissue to generate backscattered radiation. A second portion of the radiation is directed to a reflector to generate reference radiation. The backscattered radiation and the reference radiation are detected to produce an interference signal. The analyte concentration is calculated using the interference signal.
In other respects, the analyte concentration may include glucose concentration.
In another respect, the invention is a method for measuring glucose concentration within a tissue. Radiation backscattered from the tissue and reference radiation are detected to generate an optical coherence tomography (OCT) signal. The glucose concentration within the tissue is determined using a slope of the OCT signal.
In other respects, a wavelength of the radiation backscattered from the tissue may be substantially equal to a wavelength of the reference radiation. Using the slope may include correlating the slope with an optical property of the tissue. Using the slope may include correlating the slope with a morphological property of the tissue. Using the slope may include correlating a percentage change in the slope with a change in glucose concentration.
In another respect, the invention is method for measuring analyte concentration within a tissue. A probe is implanted within the tissue, the probe being configured to alter an optical coherence tomography (OCT) signal of the tissue. An OCT signal of the tissue is generated, the OCT signal being altered by the probe. A change in slope of the OCT signal is correlated with the analyte concentration within the tissue.
In other respects, the probe may be configured to increase a sensitivity of the OCT signal.
In another respect, the invention is a computer readable media containing program instructions for measuring glucose concentration within a tissue. The computer readable media includes instructions for storing an optical coherence tomography (OCT) signal in memory and instructions for determining the glucose concentration within the tissue using the signal.
In other respects, the media may be stored within an OCT apparatus. The media may be stored within a personal computer. The media may be stored within a hand-held computing device. The instructions for determining the glucose concentration may include instructions for determining a slope of the OCT signal and for determining the glucose concentration using the slope. The instructions for determining the glucose concentration may include instructions for correlating a change in the slope with an optical or morphological change in the tissue.